Geneticists warn that biology is not destiny. A person's family tree contains thousands of ancestors, and DNA evidence that one may have been Hebrew (or Armenian or Bolivian or Nigerian) means very little unless the person decides to embrace the implication, as Sanchez has done. He sees no conflict between his disparate religious traditions. "Some of us believe we can practice rituals of crypto-Judaism and still be good Catholics," he says. He keeps a menorah in a prominent place in his parish church and says he adheres to a Pueblo belief or two for good measure.

At the Albuquerque meeting, the new evidence about 185delAG prompted discussion not only among academics but also among some of the subjects. Robert Martinez, no immediate relation to Beatrice Wright, teaches history at a high school near Albuquerque. During his summer vacations he helps Hordes sift through municipal and church records in Latin America and Europe, studying family histories and looking for references to Judaism. He traces his roots to members of the first expedition to New Mexico, led by Juan de Oñate, in 1598. The Spanish explorer himself had converso relatives, Hordes has found, and included conversos in the expedition.

When he went to work as Hordes' assistant ten years ago, Martinez, who is 45, was well aware of the disease in his family: several relatives have had breast or ovarian cancer. "Of course, I'd always heard about the cancer in our family on our mom's side," he says. "And then two of my sisters were diagnosed within months of each other." Both women tested positive for 185delAG and have since died. "I carry the mutation too," he says.

The Jewish connection caused no stir in his family, he says. "Me, I'm open. I want to know, Who am I? Where am I? We're a strange lot, New Mexicans. We refer to ourselves as Spanish, but we have Portuguese blood, Native American, some black too. We descend from a small genetic pool, and we're all connected if you go back far enough."

Teresa Castellano, the genetic counselor, has spent time in the San Luis Valley explaining BRCA to community leaders, patients and others. BRCA carriers, she tells them, have up to an 80 percent risk of developing breast cancer, as well as a significant risk of ovarian cancer. If a woman tests positive, her children would have a 50-50 chance of acquiring the flawed gene. BRCA mutations are passed down by men and women alike. If a family has mainly sons, the threat to the next generation may be masked.

A year and a half ago, Castellano got a call from a laboratory technician advising her of another patient with a connection to the 185delAG mutation. The patient's family had roots in the San Luis Valley and northern New Mexico. Their name was Valdez. At the top of the pedigree were eight siblings, two of whom, sisters, were still living. In the next generation were 29 adult children, including 15 females. Five of the 15 women had developed breast or ovarian cancer. Then came an expanding number of grandchildren and great-grandchildren, who were as yet too young for the disease but who might have the mutation. Only one or two members of the disparate clan still lived in the valley.

Ironically, Castellano's initial patient, Therese Valdez Martinez, did not carry the mutation herself. Her breast cancer was a "sporadic" case, not associated with a known mutation. But Therese's sister Josephine and her first cousin Victoria had died of ovarian cancer. Their DNA, retrieved from stored blood samples, tested positive for 185delAG. "Something's going on with our family," Therese said. "We need to wake up."

Castellano offered to hold counseling sessions with members of the Valdez extended family in April 2007. With Therese's backing, she sent out 50 invitations. A total of 67 people, including children, attended the session in a hospital conference room in Denver. Therese said, "One cousin—he won't come. He doesn't want to know. To each his own."

The tables were arranged in a U-shape, rather like the mountains around the valley. Castellano stood at the open end. She pointed out that in addition to breast and ovarian cancer the Valdez family had several cases of colon cancer. "There's some risk, it appears," Castellano said, "and therefore everyone in the family should have a colonoscopy at age 45." That caused grumbling among her listeners.

"This family has a lot of ovarian cancer," she went on, "but appears not to have a breast cancer case under age 35. So we think the age for women for starting their annual mammograms should be 30 to 35. We recommend that our '185' families do it by MRI every year. And if you do have 185," she added bluntly, "get your ovaries out at age 35."

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